South Korean police have raided the office of President Yoon Suk Yeol over his role in declaring martial law last week – a move that plunged Asia’s fourth-biggest economy into crisis and caused alarm among its allies.

South Korea’s Yonhap news agency said the search on Wednesday was part of an attempt by law enforcement agencies to establish whether Yoon’s actions, supported by other senior figures in his administration, amounted to insurrection – a crime that does not carry presidential immunity and can carry the death penalty.

A special investigation unit confirmed it raided the presidential office and other agencies. “The special investigation team has conducted a raid on the presidential office, the National Police Agency, the Seoul Metropolitan Police Agency, and the National Assembly Security Service,” the unit said in a message sent to Agence France-Presse.

News of the raid came as officials said that Yoon’s former defence minister, Kim Yong-hyun, had attempted suicide while in custody at a detention centre in Seoul, where he had been held since Sunday.

Kim, who was formally arrested earlier Wednesday after a court approved a warrant for him on allegations he played a key role in a rebellion and abuse of power, was in a stable condition, Shin Yong-hae, commissioner-general of the Korea Correctional Service, told lawmakers.

Kim became the first person arrested over the 3 December martial law decree and now faces charges including “engaging in critical duties during an insurrection” and “abuse of authority to obstruct the exercise of rights”.

A spokesperson for the Seoul Central District Court told AFP that the formal arrest of Kim came amid concerns that evidence might be destroyed.

Two top police officials were also taken into custody in the early hours of Wednesday, as the investigation into the political turmoil caused by the martial law declaration gathered pace.

At least several hundred protesters rallied late on Tuesday outside the National Assembly, waving glow sticks and holding signs that read, “Impeach Yoon Suk Yeol, the insurrection criminal.”

The offices of ruling party lawmakers were being vandalised, local media reported on Tuesday, with one image showing a door covered in what appeared to be ketchup, and eggs and flour scattered on the floor.

Protesters also were sending condolence flowers to the offices, typically reserved for funerals, to express their opposition to the boycott, with signs reading “insurrection accomplices”.

Local police in Seoul’s Dobong district told AFP that an unspecified “weapon” was found in front of PPP lawmaker Kim Jae-sub’s residence, and he has requested additional security.

Yoon suspended civilian rule a week ago and sent special forces and helicopters to parliament, before lawmakers forced him to rescind the decree in a country assumed to be a stable democracy.

Kim was contrite on Tuesday, saying through his lawyers that “all responsibility for this situation lies solely with me”.

He “deeply apologised” to the South Korean people and said that his subordinates were “merely following my orders and fulfilling their assigned duties”.

Earlier on Tuesday, Army Special Warfare Command chief Kwak Jong-geun told lawmakers that Yoon had ordered him to stop enough MPs from gathering at parliament to vote down the martial law decree.

“The president called me directly through a secret line. He mentioned that it appears the quorum has not yet been met and instructed me to quickly break down the door and drag out the people [lawmakers] inside,” Kwak said.

Lawmakers passed a motion on Tuesday to appoint a special counsel to investigate the martial law case.

Yoon’s ruling party said it is forging a “resignation roadmap” that reportedly could see him step down in February or March before fresh elections, while the opposition plans to organise an impeachment vote every Saturday.

A day after Yoon was barred from travelling abroad, authorities banned more top officials from leaving the country, including Cho Ji-ho, commissioner general of the Korean National Police Agency, police told AFP.

Cho and Kim Bong-sik, the head of the Seoul Metropolitan Police Agency, were arrested early on Wednesday without warrant, Yonhap news agency reported. They can be held for up to 48 hours for questioning before a formal arrest.

Already under a travel ban are the former defence and interior ministers and martial law commander General Park An-su, who along with other top brass was grilled by lawmakers on Tuesday.

Yoon narrowly survived an impeachment effort in parliament on Saturday as tens of thousands braved freezing temperatures to call for his ouster. The motion failed after members of Yoon’s ruling People Power party (PPP) boycotted the vote, depriving the legislature of the necessary two-thirds majority.

The PPP says that Yoon, 63, has agreed to hand power to the prime minister and party chief, prompting the opposition to accuse it of a “second coup”.

A party task force was reportedly reviewing two options for a way forward, including for Yoon to resign in February with an April election, or to step down in March with a vote in May.

With the opposition holding 192 seats in the 300-strong parliament, only eight PPP members need to vote in favour of a new impeachment motion for it to pass.

Last week, two PPP lawmakers – Ahn Cheol-soo and Kim Yea-ji – voted in favour, and two more said Tuesday they would support the motion this time.

With Agence France-Presse